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The Evidence for Evolution
Chapter 21
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The Fossil Record
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Case for evolution based on two pillars:
 Evidence natural selection can produce
evolutionary change.
 Evidence from fossil record that evolution
has occurred.
Three events of fossilization:
 Organism buried in sediment.
 Calcium in material must mineralize.
 Surrounding sediment hardens.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Evidence 1-The Fossil Record
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Dating Fossils
 Radioactive isotopes have decayed more in older rocks.
- Steady decay rate allows measurement.
History
 Arraying fossils according to age provides evidence of
successive evolutionary change.
- One of strongest lines of evidence for evolution.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
The Evolution of Horses
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Modern members of
Equidae (horses, zebras,
donkeys) are descendents
of lineage originating in the
Eocene Period 55 mya.
 Earliest known members
were species in genus
Hyracotherium.
- Small size
- Multiple toes
- Small, simple teeth.
 Evolutionary change
has not occurred at a
constant rate.
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Evidence 2-Natural Selection Changes
Populations
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Darwin collected a closely
related group of 13 finch
species in the Galapagos
Islands.
 All similar except for
beak characteristics.
- Beak
correspondence
suggested to Darwin
that they were
shaped by evolution.
 Nature of
available food
supply.
Example: Beaks of Darwin’s Finches
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Natural selection continued
Peppered Moths and Industrialized Melanism
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Until the mid-nineteenth century,
Peppered Moths, Biston
betularia, had predominately
light-colored wings.
 Industrial smog helped turn
lichens on tree trunks dark.
 Subsequently, dark
individuals became
predominant.
- Predators see them!
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Second half of the twentieth
century saw widespread
implementation of pollution
controls, thus trends reversed
and light colored moths again
dominated.
But, caution must be taken, as
the selective agent could be
some factor other than wing
coloration.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Artificial Selection
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Agriculture
 Kernel characteristics of corn.
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Artificial Selection
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Domestication
 Breeds and characteristics of dogs.
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Evidence 3-The Anatomical Record
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Homology
 Structures with different appearances and
functions that all derived from a common
ancestor.
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The Anatomical Record
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Development
 Different organisms exhibit similar
embryological forms.
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The Anatomical Record
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Vestigal Structures
 Organs with no apparent modern function,
but resemble ancestral structures.
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Evidence 4-The Molecular Record
(DNA, RNA, proteins)
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Distantly related organisms are expected to
accumulate a greater number of evolutionary
differences than closely related species.
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Types of Evolution
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Convergent Evolution - Selection that favors
changes making two or more groups more
similar.
 Similar solutions to similar problems.
- Marsupial-Placental Convergence
Divergent Evolution - Selection that favors
changes making two or more groups less
similar.
 Exposure to different selective pressures.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
When two groups of the same species are
separated, changes may occur in each population
that eventually causes them to be so different that
speciation occurs
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Geographic Isolation
 separated by land formations such as rivers, mountains,
valleys, etc
Reproductive Isolation
 separated due to inability to mate with each other
- Structural, mating time is different, etc
Temporal Isolation
 Separated by time factors such as circadian rhythms
Behavioral Isolation
 Separated by behavioral differences such as courtship
dances or sounds
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Darwin’s Critics
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Evolution is not solidly demonstrated.
There are no fossil intermediates.
Intelligent Design.
Evolution violates Second Law of
Thermodynamics.
Proteins are too improbable.
Natural Selection does not imply evolution.
The irreducible complexity argument.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Review
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The Fossil Record
The Evolution of Horses
Beak’s of Darwin’s Finches
Peppered Moths and Industrial Melanism
Artificial Selection
The Anatomical Record
The Molecular Record
Convergent and Divergent Evolution
Darwin’s Critics
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies